In the mouse Mus musculus, the beta chains of adult hemoglobin are synthesized by a pair of tandemly duplicated loci, part of a cluster of at least seven related genes on chromosome 7. The species is dimorphic with respect to the number and kinds of beta globin proteins encoded by the two adult beta globin genes. In the case of the "diffuse" haplotype (Hbb-d), the two proteins differ significantly. However, the beta chains encoded by the two genes of the "single" haplotype (Hbb-s) have the same amino acid sequence, an unexpected result. It appears that the two Hbb-s adult genes have become identical by some sequence-matching process, or "gene conversion." I will investigate the origin of the gene conversion in the mouse lineage by detailed comparisons at the single nucleotide level of variants of the "single" type chromosome. I will test whether conversion events play a continuing role in maintaining the identity of these two genes, or whether it occurred only once, early in the speciation process. The experimental design combines the ability to identify variant haplotypes on the basis of linked restriction site polymorphisms and the ability to rapidly isolate these by efficient cloning and screening techniques, with methods that allow one to pinpoint single nucleotide substitutions by means short of direct sequencing, and then to determine the exact substitution by directed sequencing of only those areas where differences exist. The techniques developed for this work will be of general utility for the rapid detection and analysis of mutations and DNA sequence polymorphisms in any organism. This project is the start of a systematic study of DNA sequence evolution of the beta globin cluster in Mus musculus and related mice. To understand evolution at the nucleotide level, one must first understand the variability that exists within a species: the number and kinds of nucleotide differences that exist between alleles, between copies, between genes that are corrected against one another, between genes that are not, and between genes that have recently become genetically isolated.